The present invention relates to methods for growing high-quality, defect-free heteroepitaxial layers on any crystal substrates, regardless of the degree of lattice mismatch between the layers and the substrates.
A long-sought dream for semiconductor material research is to find methods for growing high-quality epitaxial layers on essentially any substrates regardless of the degree of lattice mismatch. However, the analysis of strain energy in a pseudomorphic material system suggests that this dream is unlikely to come true because threading dislocations will form when the epilayer thickness is well above the critical thickness. The concept of critical thickness has been so widely accepted by the semiconductor community that it has been used as a guiding principle for design of compound semiconductor material systems.
Recently, the emergence of compliant substrates raised hopes of lifting the constraint of critical thickness. By making the substrate compliant to an epitaxial layer grown on top, it is theoretically possible to grow threading dislocation free heteroepitaxy. One promising compliant substrate technology developed by the inventor involves bonding an ultra-thin semiconductor layer to a bulk crystal with an angle between their crystal axes, thereby forming a so-called twist-bonded compliant substrate. Experimental results have shown that threading dislocation free InGaP, InGaAs and InSb layers can be grown on such twist-bonded GaAs compliant substrates with a lattice mismatch as large as 15% in some cases. Other compliant substrates may have an SOI structure or use other thin film and bulk crystal bonding techniques.
In spite of the encouraging initial results obtained from compliant substrates, putting very thin (say 100 .ANG.) single crystal semiconductor layers on a bulk crystal is a very challenging and sometimes costly task. For low cost devices such as color LEDs, solar cells and solid state sensors, substrate cost becomes a significant part of the device cost. In such situations, the compliant substrate approach will have to face a trade-off between the device cost and performance. Thus, the most ideal scenario would be if high-quality heteroepitaxial layers could be formed on any commercial semiconductor substrates, such as Si and GaAs substrates, without having to perform any pre-growth processing or treatment of the substrates.